Fuel injectors for both diesel and gasoline engines have various parts that often show wear and impede the performance of the injector before other injector parts show wear. Such fuel injectors are usually, but not always located and seated in a tapered hole in the center of a cylinder head. The upper external working parts of the injector are lubricated by oil from the end of the injector rocker arm adjusting screw. Most of the internal working parts are lubricated and cooled by the flow of fuel oil through the injector.
One of the internal working parts subject to wear is the plunger. The plunger is responsible for the proper atomization of the fuel which is accomplished by the high pressure created during the downward stroke of the plunger, which forces the fuel past a valve and out through spray holes in the injector tip. The plunger is placed in motion within the fuel injector by an engine cam acting through a rocker arm and plunger follower. Rotation of the plunger is accomplished by a rack and gear system linked to the engine governor that controls the quantity of fuel to be injected into the cylinder during each stroke.
The plunger includes helices formed near the bottom of the plunger to control the opening and closing of the fuel ports within the bushing in which the plunger operates. The helices are typically machined into the outer circumference of the plunger surface. As the plunger moves past the fuel ports the edges of the helices tend to wear. Typically, the wear results in rounded edges that retard the performance of the engine. Additionally, the profile or helix angle of the helix cannot be changed with changing the plunger.
Thus, what is needed is a method and apparatus for providing a helix that is durable and capable being changed without the need for replacing the plunger.